In this paper, an efficient strategy for the synthesis of graphene nanobelt-titanium dioxide/graphitic carbon nitride (graphene-TiO2/g-C3N4) heterostructure photocatalyst was applied to fabricate a kind of visible-light-driven photocatalyst. The heterostructure shows higher absorption edge towards harvesting more solar energy compared with pure TiO2 and pure g-C3N4 respectively. Furthermore, the as-prepared graphene-TiO2/g-C3N4 heterostructure can show enhanced photocatalytic activity under visible-light irradiation. These outstanding performances of photocatalytic activities for graphene-TiO2/g-C3N4 composites can be attributed to the heterojunction interfaces which can separate the electron-hole pairs and impede the recombination of electrons and holes more efficiently. This study conclusively demonstrates a facile and environmentally friendly new strategy to design highly efficient graphene-TiO2/g-C3N4 heterostructure photocatalytic materials for potential applications under visible-light irradiation.
Asymmetric capacitor based on TiO2 with the size range from 90 to 410 nm and mesoporous MnO2 (ca. 200–380 nm) electrodes has been successfully constructed and characterized in LiClO4 aqueous electrolyte. The samples of both metal oxides were fully characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDX), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), N2 adsorption-desorption, and so on. The electrochemical capacitive performances of both electrode materials were evaluated by cyclic voltammetry and galvanostatic charge-discharge in 1 mol/L LiClO4 with a working voltage of 2.0 V. The discharge profile of the asymmetric capacitor exhibited an excellent capacitive behavior and good cycling stability after 2000 cycles. Moreover, the TiO2//MnO2 asymmetric capacitor possesses both higher energy density and power density (7.7 Wh/kg, 762.5 W/kg) than that of Maxsorb//Maxsorb symmetrical capacitor (7.0 Wh/kg, 400.0 W/kg).
Graphical abstract A novel asymmetric capacitor based on TiO2 and mesoporous MnO2 electrodes has been successfully constructed and characterized in LiClO4 aqueous electrolyte.
Rare-earth-based infinite coordination polymer (RE-ICP) spheres with diameters ranging from 50 nm to 2 μm have been prepared using meso-2,3-dimercaptosuccinic acid (DMSA) as ligand under hydrothermal conditions. RE2O2SO4 microspheres with similar morphology were obtained by calcining the corresponding RE-ICP spheres. However, as for Ce-ICP and Sc-ICP, CeO2 and Sc2O3 were obtained. The products were characterized using X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, infrared spectroscopy, laser Raman spectrometry, and energy-dispersive X-ray spectrum. Elemental analysis and inductive coupled plasma atomic emission spectrometer were adopted to study the composition of the Eu-ICP. To explore their potential applications, several samples of the products were selected and their properties were investigated. The Eu-ICP and Eu2O2SO4 microspheres give strong red emissions when excited with a 394-nm ultraviolet light. Furthermore, the Eu-ICP displays a high selectivity for Fe(III). The obtained CeO2 has a strong absorption in the UV region and the Gd2O2SO4 microspheres show paramagnetic behavior.
CeO2 and Fe2O3 co-modified titanate nanosheet (Fe2O3/CeO2@TNS) was prepared by one-pot hydrothermal method; the photocatalyst exhibited large surface area with CeO2 and Fe2O3 particles well dispersed on the surface. The results of XRD, BET, and Raman proved that the CeO2 and Fe2O3 introduced in the TNS influenced its structure evolution from 3D to 2D. The modification resulted in a shift of the absorption edge toward a longer wavelength and the band gap reduced to 2.87 eV. The three-component systems performed excellent photocatalytic activity and cycle stability on phenol and methyl blue (MB) solution under sunlight; nearly total phenol and MB were degraded in dozens of minutes. And the reaction rate constant (K) of Fe2O3/CeO2@TNS on phenol degradation was 1.77, 3.25, 4.88, and 13-fold of Fe2O3@TNS, CeO2@TNS, bare TNS, and P25, respectively. The enhanced photocatalytic activity could be ascribed to the efficient separation of photogenerated pairs through the formation of tandem n-n-n heterojunction among the three-component systems. This work will be useful for the design of other tandem n-n-n heterojunction photocatalytic systems for application in energy conversion and environmental remediation.
The Br-doped hollow TiO2 photocatalysts were prepared by a simple hydrothermal process on the carbon sphere template following with calcination at 400 °C. The structure and properties of photocatalysts were characterized by X-ray diffraction, Raman spectrum, scanning electron microscope, transmission electron microscopy, N2 desorption–adsorption, UV–Vis spectroscopy, and X-ray photoelectron spectroscopy. The TiO2 hollow spheres are in diameter of 500 nm with shell thickness of 50 nm. The shell is composed of small anatase nanoparticles with size of about 10 nm. The TiO2 hollow spheres exhibit high crystalline and high surface area of 89.208 m2/g. With increasing content of Br doping, the band gap of TiO2 hollow spheres decreased from 2.85 to 1.75 eV. The formation of impurity band in the band gap would narrow the band gap and result in the red shift of absorption edge from 395 to 517 nm, which further enhances the photocatalytic activity. The appropriate Br doping improves the photocatlytic activity significantly. The TiO2 hollow spheres with 1.55% Br doping (0.5Br-TiO2) exhibit the highest photocatalytic activity under full light. More than 98% of RhB, MO, and MB can be photodegraded using 0.5Br-TiO2 with concentration of 10 mg/L in 40, 30, and 30 min, respectively. The degradation rate of Br-doped photocatalysts was 40% faster than undoped ones.
Carbon-coated ZnFe2O4 spheres with sizes of ~110–180 nm anchored on graphene nanosheets (ZF@C/G) are successfully prepared and applied as anode materials for lithium ion batteries (LIBs). The obtained ZF@C/G presents an initial discharge capacity of 1235 mAh g?1 and maintains a reversible capacity of 775 mAh g?1 after 150 cycles at a current density of 500 mA g?1. After being tested at 2 A g?1 for 700 cycles, the capacity still retains 617 mAh g?1. The enhanced electrochemical performances can be attributed to the synergetic role of graphene and uniform carbon coating (~3–6 nm), which can inhibit the volume expansion, prevent the pulverization/aggregation upon prolonged cycling, and facilitate the electron transfer between carbon-coated ZnFe2O4 spheres. The electrochemical results suggest that the synthesized ZF@C/G nanostructures are promising electrode materials for high-performance lithium ion batteries.
One-dimensional Ce3+-doped Li4Ti5O12 (Li4Ti5?xCexO12, x?=?0, 0.01, 0.02, and 0.05) sub-microbelts with the width of approximately 500 nm and thickness of about 200 nm have been synthesized via the facile electrospinning method. The structure and morphology of the as-prepared samples are characterized by XRD, TEM, SEM, BET, HRTEM, XPS, and AFM. Importantly, one-dimensional Li4Ti5O12 sub-microbelts can be well preserved with the introduction of Ce3+ ions, while CeO2 impurity is obtained when x is greater than or equal to 0.02. The comparative experiments prove that Ce3+-doped Li4Ti5O12 electrodes exhibit the brilliant electrochemical performance than undoped counterpart. Particularly, the reversible capacity of Li4Ti4.98Ce0.02O12 electrode reaches up to 139.9 mAh g?1 and still maintains at 132.6 mAh g?1 even after 100 cycles under the current rate of 4 C. The superior lithium storage properties of Li4Ti4.98Ce0.02O12 electrode could be attributed to their intrinsic structure advantage as well as enhanced overall conductivity.
In flame spray pyrolysis (FSP), the generation of uniform nanoparticles can be quite challenging due to difficulties in controlling droplet sizes during liquid spraying and uneven flame temperature. Here, we report a method to produce relatively uniform nanocrystals of a Tb3+ doped Y2O3 phosphor. In ethanol, metal nitrate precursors were simply mixed with organic surfactants to form a homogeneous solution which was then subjected to FSP. Depending on relative concentrations of the surfactant (oleic acid) to the metal precursors (yttrium and terbium nitrates), different sizes and morphologies of Y2O3:Tb3+ particles were obtained. By adjusting the surfactant concentration, Y2O3:Tb3+ crystals as small as 20~25 nm were acquired. X-ray diffraction and transmittance electron microscopy were used to prove that as-synthesized nanoparticles were highly crystalline due to the high temperature of FSP. X-ray photoelectron spectroscopy revealed that terbium dopants were well distributed throughout Y2O3 particles and a small portion of carbonate impurities were remained on the surface of particles, presumably originated from incomplete combustion of the organic surfactants. Photoluminescence (PL) spectra of Y2O3:Tb3+ nanocrystals exhibited a green light emission ensuring that the terbium doping was successfully occurred. However, when post-annealing was performed on the nanocrystals, their PL was dramatically enhanced indicating that quenching centers such as carbonate impurities and surface defects may have been removed by the annealing process. Owing to the continuous processability of FSP, this current method can be a practical way to produce nanoparticles in a large quantity. The obtained Y2O3:Tb3+ nanocrystals were used to fabricate a transparent film with poly-ethylene-co-vinyl acetate (poly-EVA) polymer, which was suitable for a spectral converting layer for a solar cell.
In this study, the magnetically recyclable Fe3O4@C/BiOBr heterojunction with enhanced visible light-driven photocatalytic ability was obtained by two-step solvothermal method. The phase, morphology, and structure of the samples were investigated by XRD, FESEM, HRTEM, and XPS. The Fe3O4@C/BiOBr heterojunction was composed of Fe3O4@C sphere and BiOBr microsphere with diameters of 200 nm and 1000 nm, respectively. The photocatalytic performance of Fe3O4@C/BiOBr composite for RhB was examined under visible light irradiation. The photocatalytic activity of Fe3O4@C/BiOBr composite was much higher than that of pure BiOBr and Fe3O4@C. After 35 min of irradiation, 97% of RhB could be removed with the Fe3O4@C/BiOBr photocatalyst. Based on radical trapping experiments of active species, the mechanism of enhanced photocatalytic performance was proposed. In addition, the superparamagnetic property of the photocatalyst not only allows its easy recyclability by an external magnetic field but also maintains high photocatalytic activity after five cyclic experiments.
A facile and efficient one-pot method for the synthesis of well-dispersed hollow CuFe2O4 nanoparticles (H-CuFe2O4 NPs) in the presence of cellulose nanocrystals (CNC) as the support was described. Based on the one-pot solvothermal condition control, magnetic H-CuFe2O4 NPs were in-situ grown on the CNC surface uniformly. TEM images indicated good dispersity of H-CuFe2O4 NPs with uniform size of 300 nm. The catalytic activity of H-CuFe2O4/CNC was tested in the catalytic reduction of 4-nitrophenol (4-NP) in aqueous solution. Compared with most CNC-based ferrite catalysts, H-CuFe2O4/CNC catalyst exhibited an excellent catalytic activity toward the reduction of 4-NP. The catalytic performance of H-CuFe2O4/CNC catalyst was remarkably enhanced with the rate constant of 3.24 s?1 g?1, which was higher than H-CuFe2O4 NPs (0.50 s?1 g?1). The high catalytic activity was attributed to the introduction of CNC and the special hollow mesostructure of H-CuFe2O4 NPs. In addition, the H-CuFe2O4/CNC catalyst promised good conversion efficiency without significant decrease even after 10 cycles, confirming relatively high stability. Because of its environmental sustainability and magnetic separability, H-CuFe2O4/CNC catalyst was shown to indicate that the ferrite nanoparticles supported on CNC were acted as a promising catalyst and exhibited potential applications in numerous ferrite based catalytic reactions.
Previous studies on the fate of engineered nanoparticles (ENPs) incorporated in paints mainly focused on the release of the particles as affected by a limited number of factors or monitoring their release from natural sources. In this study, the effects of four factors (i.e., weathering duration, water pH, rainfall duration and intensity) were investigated on the release of SiO2-ENPs, Ag-ENPs, and TiO2-ENPs from paints applied on panels. The static water immersion test showed that the concentrations of studied particles all increased with weathering duration. At low and high pH, SiO2-ENPs and Ag-ENPs showed a higher release, while the release of TiO2-ENPs was relatively high at low pH. With increased simulated rainfall duration, the concentration released decreased for Si, and the opposite was observed for Ag, while no obvious correlation was noted for Ti. With greater rainfall intensity, there was increasing release of all particles. In total, the releases of Ag-ENPs and TiO2-ENPs were extremely low and within the level of 21.32–42.16 μg L?1and 0.6–2.3 μg L?1, respectively, while the values for SiO2-ENPs were in the range of 7.5–12 mg L?1. Additionally, microscopic results highlighted that SiO2-ENPs were mainly released in the form of agglomerates, and only a small fraction was below 0.1 μm. Considering these influence factors together, conclusions may be made that weathering time and rainfall duration are more important in controlling release than water pH.
TiO2 is ubiquitously present in a wide range of everyday items, both as an intentionally incorporated additive and naturally occurring constituent. It can be found in a wide range of consumer products, including personal care products, food contact materials, and textiles. Normal use of these products may lead to consumer and/or environmental exposure to TiO2, possibly in form of nanoparticles. The aim of this study is to perform a leaching test and apply state-of-the-art methods to investigate nano-TiO2 and total Ti release from five types of commercially available conventional textiles: table placemats, wet wipes, microfiber cloths, and two types of baby bodysuits, with Ti contents ranging from 2.63 to 1448 μg/g. Released particle analysis was performed using conventional and single particle inductively coupled plasma mass spectrometry (ICP-MS and spICP-MS), in conjunction with transmission electron microscopy (TEM), to measure total and particulate TiO2 release by mass and particle number, as well as size distribution. Less than 1% of the initial Ti content was released over 24 h of leaching, with the highest releases reaching 3.13 μg/g. The fraction of nano-TiO2 released varied among fabric types and represented 0–80% of total TiO2 release. Particle mode sizes were 50–75 nm, and TEM imaging revealed particles in sizes of 80–200 nm. This study highlights the importance of using a multi-method approach to obtain quantitative release data that is able to provide an indication regarding particle number, size distribution, and mass concentration, all of which can help in understanding the fate and exposure of nanoparticles.
Metal nanoparticles have been combined with magnet metal–organic frameworks (MOFs) to afford new materials that demonstrate an efficient catalytic degradation, high stability, and excellent reusability in areas of catalysis because of their exceptionally high surface areas and structural diversity. Magnetic MxOy@N-C (M = Fe, Co, Mn) nanocrystals were formed on nitrogen-doped carbon surface by using 8-hydroxyquinoline as a C/N precursor. The Co@N-C, MnO@N-C, and Fe/Fe2O3@N-C catalysts were characterized by X-ray diffraction (XRD), Raman, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), N2 adsorption/desorption, and X-ray photoelectron spectroscopy (XPS). The catalytic performances of catalysts were thoroughly investigated in the oxidation of aniline solution based on sulfate radicals (SO4?.) toward Fenton-like reaction. Magnetic MxOy@N-C exhibits an unexpectedly high catalytic activity in the degradation of aniline in water. A high magnetic MxOy@N-C catalytic activity was observed after the evaluation by aniline degradation in water. Aniline degradation was found to follow the first-order kinetics, and as a result, various metals significantly affected the structures and performances of the catalysts, and their catalytic activity followed the order of Co > Mn > Fe. The nanoparticles displayed good magnetic separation under the magnetic field.
This paper reported a one-step synthesis of Ag2S/Ag@MoS2 nanocomposites and its applications in the surface-enhanced Raman scattering (SERS) detection and photocatalytic degradation of organic pollutants. The nanocomposites were well characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), cyclic voltammograms (CV), the Brunauer-Emmett-Teller (BET), and Fourier transforms infrared spectra (FTIR). The AgNPs were uniformly dispersed on the MoS2 nanosheets and the particle size of the AgNPs was about 10–30 nm. These Ag2S/Ag@MoS2 nanocomposites offered sensitive SERS signals for the detection of R6G with the limit of detections as low as 10?10 M. The photocatalytic activity of the composite catalyst was studied by the degradation of methylene blue (MB) dye under light illumination. The apparent rate constant of MB degradation for the obtained catalyst could reach 6.6?×?10?2 min?1, indicating that the novel Ag2S/Ag@MoS2 nanocomposites can be explored for organic pollutant’s detection and degradation.
Mo-doped V2O5 hierarchical nanorod/nanoparticle core/shell porous microspheres (MVHPMs) were prepared via a simple hydrothermal approach using ammonium metavanadate and ammonium molybdate as precursors followed by a thermal annealing process. The samples were characterized by XRD, SEM, TEM, EDS, and XPS carefully; it confirmed that porous microspheres with uniform Mo doping in the V2O5 matrix were obtained, and it contains an inner core self-assembled with 1D nanorods and outer shell consisting of nanoparticles. A plausible growth mechanism of Mo-doped V2O5 (Mo-V2O5) porous microspheres is suggested. The unique microstructure made the Mo-V2O5 hierarchical microspheres a good cathode material for Li-ion battery. The results indicate the synthesized Mo-V2O5 hierarchical microspheres exhibit well-improved electrochemical performance compared to the undoped samples. It delivers a high initial reversible capacity of 282 mAh g?1 at 0.2 C, 208 mAh g?1 at 2 C, and 111 mAh g?1 at 10 C, and it also exhibits good cycling stabilities; a capacity of 144 mAh g?1 is obtained after 200 cycles at 6 C with a capacity retention of >?82%, which is much high than that of pure V2O5 (95 mAh g?1 with a capacity retention of 72%).
Solution combustion synthesis (SCS) is an effective and rapid method for synthesizing nanocrystalline materials. However, the control over size, morphology, and microstructure are rather limited in SCS. Here, we develop a novel ultrasonic-assisted solution combustion route to synthesize the porous and nano-sized Na3V2(PO4)3/C composites, and reveal the effects of ultrasound on the structural evolution of NVP/C. Due to the cavitation effects generated from ultrasonic irradiation, the ultrasonic-assisted SCS can produce honeycomb precursor, which can be further transformed into porous Na3V2(PO4)3/C with reticular and hollow structures after thermal treatment. When used as cathode material for Na-ion batteries, the porous Na3V2(PO4)3/C delivers an initial discharge capacity of 118 mAh g?1 at 0.1 C and an initial coulombic efficiency of 85%. It can retain 93.8% of the initial capacity after 120 cycles at 0.2 C. The results demonstrate that ultrasonic-assisted SCS can be a new strategy to design crystalline nanomaterials with tunable microstructures.
Graphical abstract Porous and nano-sized Na3V2(PO4)3/C composites with reticular and hollow structures are synthesized by an ultrasonic-assisted solution combustion route due to the cavitation effects, and exhibit excellent electrochemical performance as cathode in sodium ion battery.
This work reported a novel kind of CdTe quantum dot (QD) decorated mesoporous SiO2 (m-SiO2/QD) hybrid hollow nanoparticles for carrying photodynamic therapy (PDT) reagent. Both rod-like and spherical nanoparticles were prepared by using different shaped templates. Due to the porous shell and hollow interior, the hybrid m-SiO2/QD hollow nanorod with 360 nm long and 120 nm in diameter was selected for carrying zinc(II) phthalocyanine (ZnPc) photosensitizing molecules (61 mg/g) since the generated reactive 1O2 could be easily delivered out of the hollow particles through the porous shell (BET area 251 cm2/g). It was found that the m-SiO2/QD-ZnPc hollow nanorods exhibited a good PDT activity and showed effective photocytotoxicity for the cancer cells. Because of the porous nature, fluorescence characteristic, and excellent storage ability, the m-SiO2/QD hybrid hollow particles possessed broad potential in the fluorescent labeled PDT.
Graphic abstract m-SiO2/QD hybrid hollow particles with different morphologies could be successfully synthesized by using the templating method and they could be used as carriers for photodynamic therapy reagents.
In the synthesis of nanostructures by pulsed laser deposition (PLD), a crucial role is played by the environmental deposition pressure and the substrate temperature. Due to the high temperature of nanoparticles (NPs) at landing, other factors may determine the structure of the resulting aggregates. Here, Au and TiO2 nanostructures are obtained by non-thermal fs-PLD in ambient conditions. On Si(100), only TiO2 NPs form fractals with areas up to ~ 1 × 106 nm2, while on quartz Au NPs also form fractals with areas up to ~ 5 × 103 nm2, a much smaller size with respect to the TiO2 case. The aggregation is described by a simple diffusive model, taking into account isotropic diffusion of the NPs, allowing quantitative simulations of the NPs and fractal area. The results highlight the key role of substrate thermal conductivity in determining the formation of fractals.
The temperature-dependent field cooling (FC) and zero-field cooling (ZFC) magnetizations, i.e., MFC and MZFC, measured under different magnetic fields from 500 Oe to 20 kOe have been investigated on two exchange–spring CoFe2O4/CoFe2 composites with different relative content of CoFe2. Two samples exhibit different magnetization reversal behaviors. With decreasing temperature, a progressive freezing of the moments in two composites occurs at a field-dependent irreversible temperature Tirr. For the sample with less CoFe2, the curves of ?d(MFC ? MZFC)/dT versus temperature T exhibit a broad peak at an intermediate temperature T2 below Tirr, and the moments are suggested not to fully freeze till the lowest measuring temperature 10 K. However, for the ?d(MFC ? MZFC)/dT curves of the sample with more CoFe2, besides a broad peat at an intermediate temperature T2, a rapid rise around the low temperature T1~15 K is observed, below which the moments are suggested to fully freeze. Increase of magnetic field from 2 kOe leads to the shift of T2 and Tirr towards a lower temperature, and the shift of T2 is attributable to the moment reversal of CoFe2O4.
Graphical abstract CoFe2O4/CoFe2 composites with different relative content of CoFe2 were prepared by reducing CoFe2O4 in H2 for 4 h (S4H) and 8 h (S8H). The temperature-dependent FC and ZFC magnetizations, i.e., MFC and MZFC, under different magnetic fields from 500 Oe to 20 kOe have been investigated. Two samples exhibit different magnetization reversal behaviors. With decreasing temperature, a progressive freezing of the moments in two composites occurs at field-dependent irreversible temperature Tirr. For the S4H sample, the curves of ?d(MFC ? MZFC)/dT versus temperature T exhibit a broad and field-dependent relaxing peak at T2 below Tirr (figure a), and the moments were suggested not to fully freeze till the lowest measuring temperature 10 K. However, for the S8H sample, it exhibits the reentrant spin-glass state around 50 K, as evidenced by a peak in the MFC curve (inset in figure b) and as a result of the cooperative effects of the random anisotropy of CoFe2O4, exchange–spring occurring at the interface of CoFe2O4 and CoFe2 together with the inter-particle dipolar interaction (figure c); in ?d(MFC ? MZFC)/dT curves, besides a broad relaxing peat at T2, a rapid rise around the low-temperature T1~15 K is observed, below which the moments are suggested to fully freeze. Increase of magnetic field from 2 kOe leads to the shift of T2 and Tirr towards a lower temperature, and the shift of T2 is attributable to the moment reversal of CoFe2O4.
Perovskite solar cell is a kind of revolutionary investigation in the field of renewable energy which is capable of mitigates the deficiencies of silicon solar cell and its uprising efficiency can bring blessing to society. The presence of lead (Pb) in perovskite solar cell can make worst and negative impact on environment and is not desirable for our society. In this paper, general plans are anticipated by replacement of Pb with tin (Sn) in open atmosphere to fabricate the CH3NH3SnCl3 photovoltaic cells in chlorine (Cl)-rich environment. Excess uses of Cl has positive influences on morphological growth of the film and it also suppresses the oxidation tendency of tin (Sn) with existing oxygen in atmosphere and maintains same chemical atmosphere as bulk. Various characterization tools like X-ray diffraction, scanning electron microscope (SEM) have been used to study the effect of annealing temperature on crystal stricture, phase formation, impurities, and morphologies of the film. Finally, photovoltaic performance was reported using the solar simulator under 1.5 sun illumination.
